Tree Surgeons Required – Human Family Tree Needs Pruning

Between 3 – 2 million years ago there lived a range of early human forms. At present, there are as many as a dozen or so named hominin species positioned in this time-frame. New evidence calls into question the existence of almost all of them.

Do you know you’re A. aferensis from your H. rudolfensis? If your answer to this question is no, then you might be relieved to hear that recent discoveries suggest these species, and many others, could be mere figments of researcher’s imaginations. The hominin species presently under review include Australopithecus afarensis, Australopithecus sediba, Homo habilis, Homo naledi and Homo rudolfensis.

Human evolution has always been a subject plagued with external controversies and internal disputes. As noted by several prominent scientists, it is virtually impossible to find two paleoanthropologists that will agree on the species attributions of every single hominin fossil discovery. In fact, many researchers will suggest that some of attributed fossil finds are not even from hominins but should be considered as ancient apes.

When the Homo habilis was first identified as the earliest member of the Homo genus, back in the early 1960’s, it shifted the entire field of human origins research from an Asia centered model to one based on an African evolution. The initial finds, and subsequent identification, were made by Louis Leakey and his team at Olduvai Gorge in Tanzania. Though the remains were considered to have morphology suggestive of a human ancestor (advances in the jaw, teeth and hand structure) the crucial consideration in adding this find to the human family was the association of the hominin with stone tools discovered nearby. The use of worked stone tools was sufficient proof of human behavior. Consider that the very name Homo habilis means ‘handy man’.

Fossils accredited to Homo habilis stretch from 2.5 to 1.5 million years before present. Brain capacity was on average about half that of modern humans, around 610cc, although it may have ranged as high as 800cc. In many ways, this hominin was not only the earliest human ancestor, but represented the birth of an entire new field of study and the beginning of the Out of Africa Theory of human evolution.

Since that time several new species have joined the list of ancestors. Some have more evidence than others, Homo rudolfensis is an entire species existent thanks to a single skull fragment, whilst Homo naledi was identified from an entire cave crammed with fossilized bodies, at least 15 individuals among them. Identification of Homo forms has involved morphology, brain size and evidence of cultural traits, such as ritual burials as well as tool manufacturing. The problem currently manifesting is that some of the core Homo evidence, the morphological variation and the use of tools, has been found to be support a far broader inclusion of hominins, and far less separate species of them.

“A femur from a horse species was found nearby that also had similar stone tool damage, consistent with hominins dismembering and filleting the leg. As such these bones provide conclusive evidence of hominins at Bouri using stone tools 2.5 million years ago. And the only hominins we know of living at Bouri at this time is Australopithecus garhi.”- Richard Potts, director of the Human Origins Program, Smithsonian’s National Museum of Natural History

Stone tools being used by beings outside of our human family, 2.5 million years ago, is problem enough, after all, stone tools should mean inclusion into our genus. But soon after this revelation another site, near to Lake Turkana in Kenya, produced evidence of tool use that dated back to around 3.3 million years before present. That dating goes right back to the time of the first Australopithecus forms, the entire genus of at least 7 species which was considered to have preceded Homo. Surely then most of these species need to be re-classified as Homo ancestors?

A collection of hominin skulls most often attributed to a wide range of species.

The trouble does not end there. In 1999 and 2001 a collection of 1.8-million-year-old Homo erectus fossils were uncovered at Dmansi, in the Caucasus mountains of the Georgian republic, subsequently the entire field of palaeoanthropology was thrown into chaos. The first question was what why were these hominins so far from Africa, keeping in mind that African H. erectus were only dated to 1.9 million years. The worst was yet to come.

Researchers were soon blown away by the huge variation observable even among such a small collection of H. erectus skulls. Careful analysis of the five Dmansi skulls called into question the validity of several named hominin species, all those positioned on our family tree between late Australopithecus and H. erectus.

“The site of Dmanisi, Georgia, has yielded an impressive sample of hominid cranial and postcranial remains, documenting the presence of Homo outside Africa around 1.8 million years ago. Here we report on a new cranium from Dmanisi (D4500) that, together with its mandible (D2600), represents the world’s first completely preserved adult hominid skull from the early Pleistocene. D4500/D2600 combines a small braincase (546 cubic centimeters) with a large prognathic face and exhibits close morphological affinities with the earliest known Homo fossils from Africa. The Dmanisi sample, which now comprises five crania, provides direct evidence for wide morphological variation within and among early Homo paleodemes. This implies the existence of a single evolving lineage of early Homo, with phylogeographic continuity across continents.” – David Lordkipanidze, Georgian National Museum

It now appears that we need to rethink some of the very core understandings in human evolutionary research. It is starting to sound more like a singular ever evolving human form has existed for at least the better part of 4 million years, and that a dozen hominin and pre-hominin forms should be reduced to maybe three at most. This all has profound implications for how we think about the human story.